English spoken by blacks and whites in the United States is becoming increasingly different, making misunderstandings between the races more likely and adding to the isolation of the black poor in large cities, according to a study by a University of Pennsylvania linguist.

"Our results can be seen as signals of the dangerous drift of our society toward a permanent division between black and white," said William Labov, who headed the three-year study.

Several hundred conversations among groups of blacks and whites in Philadelphia were monitored under a grant by the National Science Foundation. They provide "an independent and objective measure of this drift" in language, Labov said.

The differences have reached the point that misunderstandings now are "more common than people think, [but] we seem to forget them very soon after they happen," Labov said.

For example, he said, black Philadelphia ghetto residents use the greeting, "What they say, home?" Whites, hearing the tapes of that expression, did not understand it -- specifically the use of "home" to mean a longtime friend -- and had to depend upon the context for its meaning, Labov said.

Labov compared his latest study to a similar study he did in the late 1960s and concluded that despite the use of standard English on radio and television there is more variance in dialect today, not only between blacks and whites, but also between whites who live in different cities.

The study found that local vernaculars in big cities are developing "faster than in the past." As a result, Labov said, Philadelphia speech differs more than ever from the speech of Boston, Chicago and New York.

"Secondly," he said, "we find that the black residents of Philadelphia are not participating in these changes. Instead [black] speech pattern is developing in its own direction and becoming more different from the speech of whites in the same communities. There is reason to think this is true for all the northern cities."

Labov suggested that the key impact of the differences in language is that black children increasingly are at a disadvantage when they begin school. Their teachers speak a different dialect and their books are written in a different dialect, he said.

"The main result of our present research is clear," Labov wrote in the study, "Segregation of Black and White Vernaculars," co-authored with Wendell A. Harris, a black researcher.

"Young black children from the inner city who must deal with the language of the classroom are faced with the task of understanding a form of language that is increasingly different from their own," Labov said.

He suggested that increased interaction between blacks and whites, particularly children, would help both groups increase their understanding. He said the language differences between middle-class whites and middle-class blacks are minimal, although differences in cultural signals and styles still can cause misunderstanding.

In Philadelphia and other big cities, he said, increasingly large numbers of black children in urban ghettos never meet any whites before going to school.

Labov said that while there are "a growing number of blacks moving into upper working-class and middle-class positions . . . the number of black residents in the segregated inner city is growing, and the relative position of the majority of the black community continues to grow worse."

In an interview, Labov added: "We're heading toward cities that are half black and half white, with very little communication between the two . . . . We're in danger of forming a permanent underclass, and our linguistic findings reflect that danger."

He said that the different uses of language between the races has the effect of "locking" blacks out of "important networks that lead to jobs, housing and basic rights and privileges."

The differences in the spoken language, as defined by Labov, have to do with intonation, the mechanics of speech, vocabulary, and a knowledge of what to say when.

Television has not had the anticipated effect of homogenizing speech, Labov said, because language is not learned from remote experience but from an individuals's social network, particuarly from peers.

"Speech is not influenced by television because it is not a primary influence," Labov said. "Primary influences come from the people who make a difference in your life . . . your supervisor, your coworker, your classmate."

Labov said that past usage of black English, such as heavy southern accents, dropping consonants so that "man" sounds like "ma," and constructions such as "she gone" to mean that "she has gone," have become even more distant from white speech, with new meanings and idiomatic expressions.

He said that the most pronounced addition to black speech in the last decade has been the use of the letter "s" to mark the past tense. Whites use "s" to mark the present tense, he said. An example of the black usage of the "s" would be: "Me an' Crystal usually be's aroun' Roy house in the mornin'."

Labov said that cultural and stylistic differences also compound misunderstandings. He said that whites, seeing each other across the street in Philadelphia, do not feel the need to acknowledge the meeting, while blacks would find it "most inappropriate not to speak."

Labov's work is supported by Thomas Kochman, a professor of communications at the University of Illinois at Chicago. Kochman, in his book "Black and White -- Styles in Conflict," wrote that blacks and whites often fail to communicate because they use different signals.

In an office setting, Kochman said, blacks value confrontation and argument, even to the extent of becoming emotional, as a "method of truth-seeking." He said that to blacks, the effort of confronting another person is proof that the workers involved care enough to settle the dispute. Kochman said that whites generally see confrontation as "a bad thing -- to them it is evidence of disunity."

"The white mainstream avoids confrontation because they think of, literally, physically fighting much more quickly," said Kochman.

Similarly, Kochman said in an interview, blacks and whites often misinterpret responses. If a white woman has a cast on her arm, Kochman said, she would expect coworkers to ask her how she hurt herself. A black, he said, would be offended if coworkers asked, and would view the question as an intrusion.